Nuclear reactor control room habitability system

ABSTRACT

A cooling system for a nuclear plant main Control Room Habitability System that employs a vortex tube interposed between a compressed air supply and the control room. The relatively cold air output from the vortex tube is fed into the control room or the electrical equipment room while the relatively hot air exiting the vortex tube is exhausted to the atmosphere.

BACKGROUND

1. Field

This invention pertains generally to nuclear reactor control room habitability systems and more particularly to conditioning the air intake to such systems during a station blackout.

2. Related Art

New designs of commercial nuclear powered electrical generating facilities are designed to passively shut down upon experiencing adverse operating conditions such as the loss of offsite and onsite supplied AC power. In the unlikely case of experiencing such an event it is important to protect personnel in the main control room and their data processing systems so that they can continue to monitor the reactor to assure all of the safety systems are performing correctly. For this reason, if there is a loss of AC power the main control room air conditioning system has to be passively isolated and conditioned to prevent the introduction of radioactive particulate matter and maintain a habitable environment.

Westinghouse Electric Company LLC, Cranberry Township, Pennsylvania, offers the AP1000® passive nuclear plant that has such a main Control Room Habitability System which is intended to provide fresh breathable air to the main control room under station blackout conditions, i.e., upon a loss of off-site power. The passively powered main Control Room Habitability System provides pressurization, ventilation, cooling and filtration of the control room environment following a design basis accident or loss of AC power. In the event of a design basis accident that does not interrupt AC power, the nuclear island non-radioactive ventilation system would continue to function. If AC power is lost or a control room radiation signal above a pre-selected value is received, the main Control Room Habitability System is actuated. The main Control Room Habitability System also limits the heat-up of the main control room, the safety instrumentation and control equipment rooms, and the safety equipment rooms by using the heat capacity of the surrounding structures. In the AP1000® nuclear plant design, manual and automatic actuation of the main Control Room Habitability System is achieved via the protection and safety monitoring system.

The main Control Room Habitability System supplies air to the control room from a number of compressed air storage tanks that have a sufficient supply of stored air to provide 65 plus or minus 5 SCFM (Standard Cubic Feet Per Minute) to the main control room area for at least 72 hours. As stated, operation of the main Control Room Habitability System is automatically initiated upon receipt of a radiation particulate reading above a predetermined level or iodine radioactivity set point, or a low pressurizer pressure, whereupon a safety related signal is generated to isolate the main control room from the nuclear island non-radioactive ventilation system and to initiate air flow from the main Control Room Habitability System storage tanks. Isolation of the nuclear island non-radioactive ventilation system consists of closing valves in the supply and exhaust ducts that penetrate the main control room pressure boundary. Main Control Room Habitability System air flow is initiated by a signal which opens the isolation valves in the main Control Room Habitability System supply lines.

In order to supply breathable air to the occupants of the main control room, the main Control Room Habitability System is composed of compressed air storage tanks, two air delivery flow paths, associated valves, piping, and corresponding instrumentation. The tanks contain enough breathable air to supply the required air flow to the main control room for at least 72 hours. The main Control Room Habitability System is designed in the AP1000® plant to maintain CO₂ concentration less than 0.5 percent for up to eleven main control room occupants. The compressed air storage tanks are initially pressurized to 23.4 MPa gauge. During operation of the main Control Room Habitability System, a self-contained pressure regulating valve maintains a constant downstream pressure regardless of the upstream pressure. An orifice downstream of the regulating valve is used to control the air flow rate into the main control room. The main control room is maintained at a 0.32 cm gauge positive pressure to minimize the infiltration of air-borne contaminants from the surrounding areas.

In the unlikely event that power to the nuclear island non-radioactive ventilation system is unavailable for more than 72 hours, main control room envelope habitability is maintained by operating one of the two main control room ancillary fans to supply outside air to the main control room envelope. It is desirable to enhance the cooling capability of the main Control Room Habitability System to provide more margin on the predicted control room temperature during an extended station blackout period.

Accordingly, it is an object of this invention to add to the cooling capability of a main Control Room Habitability System that does not require an external source of power.

It is a further object of this invention to provide such a cooling capability in a manner that is reliable and without any moving parts.

SUMMARY

These and other objects are achieved by a nuclear power plant equipment room passive cooling system having a stored source of compressed gas sufficiently large enough to deliver compressed gas at a pressure of approximately between 100 and 120 psi for at least two days to the equipment room. At least one vortex tube is provided having a gas inlet and a relatively cool gas outlet with the gas inlet in fluid communication with the storage source of compressed gas and the cool gas outlet in fluid communication with the nuclear plant equipment room. The cooling system has a gas regulator interposed between the storage source of compressed gas and the gas inlet for regulating the gas flow to the gas inlet to approximately between 100 and 120 psi. The vortex tube also has a relatively hot gas outlet which has a higher temperature than the relatively cool gas outlet with the hot gas outlet exhausted to the ambient environment outside of the equipment room; preferably to the atmosphere. Desirably, the gas regulator maintains the flow to the gas inlet at substantially 120 psi and the vortex tube is situated outside of the equipment room. In one embodiment, the nuclear plant equipment room is a main control room. Preferably, the vortex tube also communicates to cool the data processing systems that feed the main control room.

In another embodiment, the vortex tube comprises an array of a plurality of vortex tubes and preferably the plurality of vortex tubes are connected in parallel and are configured into an existing plant architecture.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the invention claimed hereafter can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic drawing of a nuclear power plant equipment room habitability system incorporating the vortex tube illustrated in FIG. 2; and

FIG. 2 is a schematic drawing of a vortex tube, illustrating its principal of operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The AP1000® nuclear plant design includes a main Control Room Habitability System 10 which is schematically illustrated in FIG. 1. As previously mentioned, the passively powered main Control Room Habitability System provides pressurization, ventilation, cooling and filtration of the control room environment following a design basis accident or a loss of AC power. The compressed air stored in the plant is sufficient to provide 65 plus or minus 5 SCFM to the main control room area for at least 72 hours. It is desirable to enhance the cooling capability of the main Control Room Habitability System to provide more margin on the predicted control room temperature during an extended station blackout. Since a station blackout results from a loss of AC power, the main Control Room Habitability System is designed to be a passive system and any such enhancement should also be passive. This invention employs a vortex tube 12 to accomplish such an enhancement. The advantage of using a vortex tube to enhance the main Control Room Habitability System cooling performance is that by design these devices are passive, requiring only a supply of compressed air to operate. In order to provide for the main control room's needs during a 72-hour station blackout, the main Control Room Habitability System provides compressed air stored at a maximum pressure of 4,000 psi in 32 tanks. The compressed air in the tanks 22 is connected in parallel to an inlet line 30 which feeds the compressed air through a valve and regulator 28 that reduces the pressure to a range of approximately 100 to 125 psig regardless of the input pressure to the regulator so long as it is above the outlet pressure. The outlet of the regulator 28 is then fed to an inlet 20 on the swirl chamber 18 of the vortex tube 12. The outlet of the cold end 16 of the vortex tube 12 is then fed to the equipment room 26 which preferably includes the main control room as well as the data processing equipment that feeds the main control room. The hot air stream that exits the hot end 14 of the vortex tube 12 is preferably exhausted to the atmosphere.

The vortex tube, also known as the Ranque-Hilsch vortex tube, is a passive mechanical device that separates a compressed gas into hot and cold streams. The air emerging from the “hot” end can reach temperatures of 200 degrees centigrade, and the air emerging from the “cold” end can reach minus 50 degrees Centigrade. The vortex tube has no moving parts. Pressurized gas is injected tangentially into a swirl chamber located at one end of the tube and accelerated to a high rate of rotation. Due to a conical nozzle 24 at the other end of the tube, only the outer shell of the compressed gas is allowed to escape at that end. The remainder of the gas is forced to return in an inner vortex of reduced diameter within the outer vortex. A schematic illustration of a vortex tube is shown in FIG. 2. The air storage supply 22 is pressurized between 3,300 to 4,000 psig within a plurality of storage tanks which are connected in parallel to the inlet line 30 that feeds a regulator 28 before being introduced into the swirl chamber 18 of the vortex tube 12.

There are different explanations for the cooling effect that is produced by a vortex tube and there is a debate on which explanation is more correct. What is generally agreed upon is that the air in the tube experiences mostly “solid body rotation,” which means the rotation rate (angular velocity) of the inner gas is the same as that of the outer gas. This is different from what most consider standard vortex behavior—where the inner fluid spins at a higher rate than the outer fluid. The (mostly) solid body rotation is probably due to the long length of time during which each parcel of air remains in the vortex—allowing friction between inner parcels and outer parcels to have a notable effect.

One simple explanation is that the outer air is under higher pressure than the inner air (because of the centrifugal force). Therefore, the temperature of the outer air is higher than that of the inner air.

Another explanation is that as both vortices rotate at the same angular velocity and direction, the inner vortex has lost angular momentum. The decrease of angular momentum is transferred as kinetic energy to the outer vortex, resulting in separated flows of hot and cold gas.

Commercial vortex tubes are designed for many industrial applications where a stream of cooled air is required with a temperature drop of up to 50 degrees Fahrenheit. With no moving parts, no electricity, and no refrigerant, single commercially available vortex tubes can produce cooling exceeding 10,000 BTU/hr using only filtered compressed air at 100 psi. By adjusting the supply pressure and the amount of extracted hot air, a wide range of cooling capability can be achieved. Vortex tubes have been used for the cooling of cutting tools used for machining operations where a directed supply of cool air is required. These devices have also seen commercial application for cooling cabinetry and other spaces.

The vortex tube is ideally matched for an application to an AP1000® nuclear plant design because the needed supply of pressurized air is already available, and the 65 SCFM flow rate can easily be handled by a small array of vortex tubes. Ideally, the tubes are connected in parallel. The physical size of these devices is relatively small so that incorporation into the existing plant architecture is not an issue. While other methods exist for conditioning an air supply, they are active and relatively complex requiring a source of AC power to operate. Accordingly, this invention provides an inexpensive means for improving the main Control Room Habitability System that can also condition the air in the electrical equipment room processing data for the main control room.

While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. 

What is claimed is:
 1. A nuclear power plant equipment room passive cooling system comprising: a storage source of compressed gas sufficiently large enough to deliver compressed gas at a pressure of approximately between 100 and 120 psi for at least two days to the equipment room; at least one vortex tube having a gas inlet and a relatively cool gas outlet with the gas inlet in fluid communication with the storage source and the cool gas outlet in fluid communication with a nuclear plant equipment room; and a gas regulator between the storage source of compressed gas and the gas inlet, for regulating the gas flow to the gas inlet to approximately between 100 and 120 psi.
 2. The passive cooling system of claim 1 wherein the vortex tube has a relatively hot gas outlet wherein the relatively hot gas outlet is at a higher temperature than the relatively cool gas outlet and is exhausted to the ambient environment outside the equipment room.
 3. The passive cooling system of claim 2 wherein the relatively hot gas is exhausted to the atmosphere.
 4. The passive cooling system of claim 1 wherein the gas regulator maintains the flow to the gas inlet at substantially 120 psi.
 5. The passive cooling system of claim 1 wherein the vortex tube is situated outside the equipment room.
 6. The passive cooling system of claim 1 wherein the nuclear plant equipment room is a main control room.
 7. The passive cooling system of claim 1 wherein the vortex tube comprises an array of a plurality of vortex tubes.
 8. The passive cooling system of claim 7 wherein the array of the plurality of vortex tubes are configured in parallel.
 9. The passive cooling system of claim 8 wherein the parallel array of vortex tubes are configured into an existing plant architecture. 